This PDF file contains the front matter associated with SPIE Proceedings Volume 10730, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Structured light and structured matter are two fascinating branches of modern optics that recently started having a significant impact on each other. The synergy of complex beams, such as the beams carrying an orbital angular momentum, with nanostructured engineered media is likely to bring new dimensions to the science and applications of structured light, ranging from fundamentally new regimes of spin-orbit interaction to novel ways of information encoding for the future optical communication systems. We will discuss fundamental optical phenomena at the interface of singular and nonlinear optics in engineered optical media and show that the unique optical properties of optical nanostructures open unlimited prospects to “engineer” light itself.

Atomically-thin two-dimensional (2D) materials have attracted remarkable interest in a wide range of research and applications. However, one of the main challenges is how to visualise the extremely thin films and accurately identify its layer thickness. Due to the ultimately thin thickness and the low absorption of light, many 2D films, such as graphene, graphene oxide and hexagonal boron nitride (hBN) are nearly completely transparent on most surfaces. They are only visible when deposited on specific contrast-enhancing substrates. However, there is no universal substrates which can be used to visualise all 2D materials. A substrate often can only provide enhanced visibility for a specific category of 2D materials. For instance, the oxidised Si substrates can considerably enhance the optical contrast of graphene, but produce negligible enhancing effect on hBN. It is therefore desirable to develop a general theoretical guidance on how to design contrast-enhancing substrate for any given 2D materials. Here we report a universal theoretical model which can be employed to design high-contrast substrates for any 2D materials. For a given thin film of known optical properties, the optical contrast is completely defined by the complex reflectivity of the underlying substrate. By engineering the optical properties of the underlying substrate, we fabricated a range of structures, significantly enhancing the contrast of graphene, graphene oxides and hBN. Monolayers of these transparent 2D films are readily visible (>10% contrast) on a range of substrates with metallic or dielectric materials as top surface layers. The measured optical contrasts excellently match theoretical calculations.

THz diffractive lenses have recently gathered a lot of attention as an effective alternative to conventional THz lenses which are bulky, thick, expensive and suffer from strong wavefront (geometric and chromatic) aberrations. It has already been shown that employing a direct binary search technique on the actual height profile of diffractive elements (DEs) can yield designs with better or comparable performance metrics with respect to kinoforms. Such search techniques are however, limited by their exponential time complexity in an unstructured design solution space. If the solution can be proven to exist, we can further perform a gradient descent optimization along with the binary search to overcome the time complexity required to arrive at the desired solution. The semi-analytic and measured efficiency for all diffractive lenses under both narrowband and broadband focusing is > 80% based on our modified DBS employed design prediction. The modified DBS is observed to converge much faster for both 1D and 2D diffractive lens cases (>10X) with respect to conventional direct binary search based design prediction. For 2D diffractive lenses, the figure of merit is initially high and takes a longer time to converge to the desired solution, which can be understood from the fact that the number of “dielectric” pixels in a 2D lens is much greater than its 1D analogue. Furthermore, since the direct binary search is an iterative algorithm, it convergence depends a lot on the initial random pixel height profile, which is not the case in the modified DBS method.

Optical vortex beams, including the orbital angular momentum beam (OAM) with the phase singularity and cylindrical vector beams (CVBs) with the polarization singularity, are orthogonal structured light beams providing a new degree of freedom for multiplexing optical communications. There are already several mature approaches for the OAM detection such as the fork grating and geometric optical transformation. However, the technique for efficient CVBs sorting has not been demonstrated yet. In this work, we propose and demonstrate the efficient sorting of multiple CVBs based on the anisotropic geometric optical transformation approach using the Pancharatnam-Berry optical element (PBOE) device. The device is fabricated by the photo-alignment liquid crystal (LC) in a thin film with a total pixel number of 768×768 and a pixel size of 11.7μm. Since the PBOE has the circular polarizations selective property, the device can independently modulate the left-handed circular polarized and right-handed circular polarized light components of CVB. The anisotropic geometric optical transformation is capable of transforming the CVB from the donut shape to two straight lines shape. Through the phase correction and a Fourier transform by lens focusing, the CVBs is finally converted to a single light spot with a lateral displacement proportional to the input CVBs orders. In the proof of concept experiment, we demonstrated the CVBs sorting from -10 to 10 orders with an efficiency up to 61.7%. We also demonstrated multiple coaxial CVBs demultiplexing. The CVB sorting approach shows potential applications in optical multiplexing communication.

We demonstrate optical and electrical property enhancement of solar cells using a variety of dielectric nano-resonator array coatings. First, we study close-packed silicon dioxide (SiO₂) nano-resonator arrays on top of silicon (Si) and gallium arsenide (GaAs) solar cells. From macroscale measurements and calculations, we find that absorptivity of solar cells can be improved by 20 % due to the resonant couplings of excited whispering gallery modes and the thin-film antireflection effect. Next, we image photocurrent enhancement at the nanoscale via near-field scanning photocurrent microscopy (NSPM). Strong local photocurrent enhancement is observed over each nano-resonator at wavelengths corresponding to the whispering gallery mode excitation. Finally, for better optical coupling to solar cells, we explore hybrid nano-resonator arrays combining multiple materials such as silicon dioxide, silicon nitride, and titanium dioxide. Due to higher number of photonic modes within such hybrid coatings, absorptivity is enhanced by more than 30 % in a Si solar cell.

Concentrated solar power (CSP) systems need to complement the photovoltaic (PV) technology via energy storage to better integrate solar electricity in to power grids. The efficiency of CSP systems can improve with high optical absorption in the solar spectrum regime and low emittance in the infrared (IR) spectrum, thereby reaching higher operation temperatures for lower levelized cost of energy. High-temperature, air-stable solar selective absorbers made with cermet composite materials that have optimal properties of both ceramic and metal can be the solution to this goal; however, this achievement has been difficult due to metal oxidation at high temperatures. Current state-of-the-art product such as the Pyromark 2500 black paint has a significantly high solar absorbance (α_solar=97%) in the solar spectrum regime but also has a high thermal emittance loss (ε=88%) in the IR spectrum at 750 °C.[1] Here, we demonstrate outstanding optical responses of thermodynamically-stable, high-temperature, low-cost long-term antioxidation cermet solar selective absorber coatings with MnFe₂O₄ and MnO₂ nanoparticles and silicone precursors as Si-rich matrices that undergo inter-diffusion reaction with Stainless Steel 310 (SS310). It has been shown that absorbers with MnFe₂O₄ nanoparticles have solar absorbance of ~92.5%, thermal emittance of 55%, and thermal efficiency of 88-89% posterior to annealing at 750°C for 700 hours in air, and those with MnO₂ nanoparticles have solar absorbance of ~91.5%, thermal emittance of 52.5%, and thermal efficiency of 88% posterior to annealing at 750°C for 700 hours in air. We expect that the solar selective absorber coatings with such high thermal efficiencies and high-temperature stability in air will lead to a breakthrough in the market of CSP systems.

This research investigated the preparation, characterization and supercapacitive properties of cobalt oxide-nickel oxide (CoO-NiO) microflowers incorporated with graphene oxide (GO) and reduced graphene oxide (RGO) nanosheets. These hybrid materials were easily prepared through a direct mixing of CoO-NiO powder suspended in acidic solution with the appropriate amount of GO and RGO loading to make CoO-NiO/GO and CoO-NiO/RGO hybrid samples, respectively. Then, the obtained hybrid samples were characterized by X-ray powder diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The results demonstrated that the crystalline phases and functional groups of all hybrid samples are corresponding to pristine CoO-NiO and RGO. SEM results showed that the CoO-NiO microflowers were impregnated and well-combined with both GO and rGO nanosheets. Moreover, the supercapacitive behavior of pristine CoO-NiO and all hybrid samples were studied using cyclic voltammetry (CV) technique. The results revealed that all hybrid samples exhibited much higher the current density than those of the bare CoO-NiO. Thus, this research indicates that the supercapacitive properties of CoO-NiO incorporated with both GO and RGO hybrid materials are superior to the pure CoO-NiO microflowers.

Owing to the layered geometry and the thickness-dependent bandgap, two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) exhibit unique nonlinear optical (NLO) features and have becoming intriguing and promising candidate materials for photonic and optoelectronic devices with high performance and unique functions. We have extensively investigated the layer number dependent nonlinear absorption and nonlinear refractive index of monolayer and few-layer transition metal dichalcogenides (i.e., WS2, MoS2, etc.) over broad wavelength (Vis-NIR) range. Distinct NLO responses were demonstrated that multilayer films showed saturable absorption effect, and monolayer films exhibited remarkable two-photon absorption (TPA) effect. The giant nonlinearity of WS2 and MoS2 films was ascribed to the 2D confinement, giant exciton effect and the band-edge resonance of TPA. Importantly, we show that two-photon excitation can be used to probe the movement of dark excitonic state and band-edge in layered MoS2. The nonlinear refractive index of WS2 and WSe2 semiconductor films have been characterized by using Z-scan technique with fs pulses at the wavelength of 1040 nm. There exists a dispersion of nonlinear refractive index in the WS2 films that translated from positive in the monolayer to negative in the bulk. These works have make foundations for the potentials 2D semiconductor based nonlinear photonic devices, such as optical switch, mode-locker, optical limiter, optical diode, etc.

We demonstrate the suitability of two cost efficient technologies, namely roll-to-roll hot embossing and laser-assisted hot embossing, to fabricate arrays of structures in the microscale down to the sub-100 nm range. We therefore employ polymers with a relatively moderate glass transition temperature, e.g., cyclic olefin copolymer (COC) and polystyrene (PS). We compare the two replication processes regarding their precision and cost using different 1D and 2D nanostructure gratings and microfluidic channels. All nickel shims used for the replication are fabricated in combination of electron beam or UV lithography and nickel electroforming. The replicated structures are used in different applications. The nanopillar arrays are coated with gold and integrated in the hot embossed microfluidic channels for lab-on-a-chip (LoC) surface-enhanced Raman analysis. We evaluate the as-fabricated 2D nanopillar arrays for surface-enhanced Raman spectroscopy (SERS) using solutions of rhodamine 6G as exemplary analytes. The influence of the geometrical parameters like diameter and pitch of the polymer structures as well as the influence of the gold layer thickness are discussed. 1D-gratings will be used as resonators for organic distributed feedback (DFB) lasers. Both elements, the SERS chips and the organic DFB lasers as tunable excitation source can be combined in the future to form one Raman-on-Chip optofluidic platform for sensitive detection of low-concentrated analytes in water.

Surface functionality is an increasing and crucial factor for the success and acceptance of a product. Through structured surfaces products can gain additional functions. Microstructures enable, for example, friction reduction in combustion engines or optimize the efficiency of LED-based illumination systems. Furthermore, in the area of consumer products optical and haptic functions determine essentially the product quality.

The most common way to create surface functionality in mass production are replication processes via structured mold tools. In industrial environment nanosecond pulsed laser sources are established due to their high throughput. Ultrafast laser processing still have shown their advantages characterized by highly precise ablation with minimal thermal influence. Nevertheless, the achieved productivity is still too low for industrial applications in many cases due to the low ablation rate of ultrashort pulse laser processing.

To overcome the above mentioned drawback, we investigate ultrashort pulsed laser processing using pulse bursts including pauses to avoid heat accumulation and several scaling strategies like increasing the repetition frequency and enlarging the spot size. The experiments are processed with a pulse duration of 900 fs or 2 ps for productivity reasons. Using average powers of more than 70 W an ablation rate of up to 13 mm³/min is achieved. Not only productivity benefits from burst processing with pauses, but also the surface quality gets significantly improved. The roughness of an ablated surface processed with conventional bursts for example amounts R_α = 5.19 μm while the same burst configuration including a pause produces a surface roughness of R_α = 0.51 μm.

High aspect ratio silicon was fabricated by metal-assisted chemical etching (MACE). We have fabricated zone plate with 16 nm outermost zone width and 8 μm thickness, thus achieving a very high aspect ratio up to 500. Such zone plates have the potential for high efficiency and fine spatial resolution for x-ray nanofocusing applications. High aspect ratio diamond was fabricated by reactive ion etching (RIE). We have fabricated diamond gratings with 300 nm half-pitch and more than 10 μm thickness. Diamond has more thermal conductivity than silicon. Such gratings could be used as x-ray beam splitter for free-electron laser.

We report on a fabrication route based on hot embossing lithography to replicate the surface texture of plants into large-area polymeric foils, with a view to developing multifunctional photovoltaic cover layers. Our approach is demonstrated by reproducing the complex texture of rose petals with a high fidelity from the nano-to the centimeter scale into different polymers, including poly(methyl methacrylate) (PMMA), polycarbonate (PC) and fluorinated ethylene propylene (FEP). We show that the hot embossed PMMA and PC foils, applied as a cover layer onto a copper indium gallium diselenide (Cu(In,Ga)Se₂) thin-film solar cell, improve its light harvesting properties compared to (unencapsulated) devices based on an optimized MgF₂ antireflective coating, especially at large angles of incidence (>50°). By employing a low surface free energy polymer like FEP, we further demonstrate that the textured cover layer can achieve strong hydrophobicity (with water contact angle around 135°) without any additional surface treatment. This wetting property results in droplets hitting the foil rapidly bouncing off its surface, which can be exploited for self-cleaning purposes. The bioreplication route presented herein can be extended to other biological surfaces, polymers, photovoltaic technologies or to other optical systems to introduce a light harvesting scheme operating efficiently in outdoor conditions.

A magnetron co-sputtering system was used for producing nickel-doped Ge₂Sb₂Te₅ (GST-Ni) thin films. The nickel content in the thin film was adjusted by the ratio of the plasma discharge power applied to the GST and nickel targets, as well as a physical shuttering technique to further control the nickel deposition rate. The doping concentration of the film was confirmed using Energy Dispersion Spectroscopy (EDS) technique. Results from a four-point probe measurement indicate that the nickel doping can reduce the resistivity of GST in the amorphous state by nearly three orders of magnitude. The dopant’s influence on crystallization behavior was studied by analyzing X-Ray Diffraction (XRD) patterns of the pure GST and GST-Ni at different annealing temperatures. To examine the structural changes due to the nickel dopant, the thin films were investigated with the aid of Raman scattering. Additionally, we extracted the optical constants for both the amorphous and crystalline states of undoped-GST and GST-Ni films by ellipsometry. The results indicate that at low doping concentrations nickel does not appreciably affect the optical constants, but dramatically improves the electrical conductivity. Therefore, nickel-doping of GST a viable method for designing optical devices for lower operating voltages at higher switching speeds.

Development of stimuli-interactive sensing display capable of spontaneously visualizing various external human sensible inputs has been of great interest and tremendous efforts are devoted to the visualization of nonvisible human senses such as touch, smell, taste, and sound. Field induced electroluminescence of either organic or inorganic fluorescent materials under alternating current (AC) has been extensively studied and its unique device architecture in which an emitting layer is separated with an insulator from electrode offers a new platform for designing and developing emerging stimuli-interactive displays. In this presentation, high-performance field-induced AC polymer electroluminescence (AC-PEL) devices are demonstrated with high brightness, high efficiency and color and intensity-tunability. We also present a pressure interactive AC display sensor that allows for both sensing and visualisation of pressure. Light emission upon exposure to an AC field between two electrodes is controlled by the capacitance change of the insulator arising from the pressure applied on top. Besides capacitive pressure sensing, our EL sensor allows for direct visualisation of the static and dynamic information of position, shape, and size of a pressurising object on a non-pixelated single device platform. Finally, the presentation shows that simultaneous sensing and visualization of the conductive substance is achieved when the conductive object is coupled with the light emissive material layer on our novel parallel-type AC-PEL device. A variety of conductive materials can be detected regardless of their work functions, and thus information written by a conductive pen is visualized, as is a human fingerprint with natural conductivity.

The growing interest in quantum technology applications such as laser cooling and quantum sensing has generated a large demand for narrow linewidth and high-power laser sources in the visible and near-infrared wavelength emission range. Semiconductor lasers are ideal candidates for developing these sources as they combine low cost and low-power consumption with small size and unparalleled potential for integration. This work presents experimental results on two complementary design strategies that can be effectively used to reduce the laser linewidth in a Distributed FeedBack (DFB) semiconductor laser: i) the optimisation of the epilayer structure and ii) the apodisation of the grating geometry. The design of the epilayer stack was optimised to vertically shift the optical mode towards the n-doped region so as to reduce the interaction with the more lossy p-doped region and therefore decrease the internal losses of the waveguide. Such design also reduces the modal overlap with the quantum well (QW) gain region. As predicted by the Schawlow-Townes relationship, both of these factors translate into a reduction of the laser linewidth. The DFB lasers were fabricated with a sidewall grating geometry that simplifies the fabrication process and allows to engineer the feedback profile. In this work, the gratings were apodised to alleviate the spatial hole burning, which substantially worsen the laser linewidth at high power levels. The optimisation of the epilayer and grating designs allowed to fabricate robust devices with measured linewidths as small as a few hundred kHz and power output of several tens of mW.

We study and demonstrate a Bloch-surface-wave-based nano-thin waveguide grating. The waveguide grating is characterized as a Bragg mirror at telecommunication wavelengths. The structure is a dielectric multilayer platform designed to sustain a Bloch surface wave. Such a platform is regarded as a foundation for in-plane integrated optics. The Kretschmann coupling configuration, as the most widely used approach, is utilized to excite the optical surface waves. We use multi-heterodyne scanning near-field optical microscopy to characterize the waveguide gratings in the near-field. The fabricated waveguide grating shows the expected Bragg mirror behavior with a measured reflectivity of approximately 72 % inside the photonic band gap at λ = 1553 nm.

Hydrogels with the precise three-dimensional configuration (3D hydrogels) have played important roles in the fields of tissue engineering and drug delivery, which will help to mimic the behavior of bio-inspired systems. Thus, the improvement of the spatial resolution on both the microscopic and the nanometric scale has been urgently demanded. There are some developed techniques to fabricate the 3D microstructures, however, these techniques require either high energy, strict operation environment or expensive mask. As a promising maskless and flexible photolithography technique, two-photon polymerization (TPP) is a promising protocol to achieve 3D hydrogels. However, TPP of 3D hydrogels has been hindered due to the lack of high efficient water-soluble photoinitiator. In this presentation, the development of water soluble TPP photoinitiator of high initiating efficiency, as well as its fabrication capability and the resolution will be illustrated. The high resolution of 92 nm has been achieved benefiting from the high efficency of the developed photoinitiators and the optimized optical parameters. Furthermore, the microstructures with high accuracy such as those simulating the morphology of adenovirus and red blood cell have been fabricated, demonstrating the promising fabrication capability for achieving arbitrary architectures. The design of the photoinitiators, and the TPP fabrication technique mentioned in this study would provide high potential for the futher application in the research fields of cell imaging and tissue engineering.

In this paper we present the size reduction of a 160-channel, 50-GHz Si₃N₄ based AWG-spectrometer. The spectrometer was designed for TM-polarized light with a central wavelength of 850 nm applying our proprietary “AWG-Parameters” tool. For the simulations of AWG layout, the PHASAR photonics tool from Optiwave was used. The simulated results show satisfying optical properties of the designed AWG-spectrometer. However, such high-channel count AWG features large size. To solve this problem we designed a special taper enabling the reduction of AWG structure by about 15%, while keeping the same optical properties. The technological verification of both AWG designs is also presented.

Luneburg lens is a fascinating gradient refractive index (GRIN) lens that can focus parallel light rays on a perfect geometrical point without aberration in geometrical optics, compared with conventional lens made of homogeneous dielectric materials with specially designed surfaces. Constructing a three dimensional (3D) Luneburg lens at optical frequencies is a challenging task due to the difficulty of fabricating the desired GRIN materials in the lab. Reported experimental realizations of Luneburg lens at optical frequencies are mainly based on two dimensional metamaterials structures, or plasmonic structures. Here, we present the first practical implementation of the 3D version of Luneburg lens at optical frequencies based on the effective medium approximation. The 3D Luneburg lens is designed with GRIN 3D simple cubic metamaterials (SCMs) structures, and fabricated with no-resonant dielectric metamaterials by laser direct writing method in the commercial negative photoresist IP-L. We have experimentally demonstrated the feasibility of tailoring inhomogeneous metamaterials structures to realize 3D Luneburg lens with the effective GRIN profiles. The effective refractive index has been spatially and gradually modified by tailoring the volume filling fraction of SCMs structures. Simulated and experimental results simultaneously exhibit interesting 3D ideal focusing performance of the 3D Luneburg lens for the infrared light at wavelengths of 6.25m. This study would provide the protocol for developing the 3D Luneburg lens with wide field-of-view and ideal focusing theoretically and experimentally, which would further prompt the potential applications in integrated light-coupled devices and lab-on-chip integrated biological sensors based on infrared light.

Due to its optical and structural characteristics, cerium oxide (ceria) nanoparticles have been used in wide variety of applications. This paper introduces the enhancement of visible fluorescence emission of ceria nanoparticlesthrough adding plasmonicgold nanoparticles (Au NPs) under violet excitation. Au NPs lead to enhance the formation of tri-valent ionization states of cerium ions with corresponding oxygen vacancies formation. In addition, the coupling between plasmonic waves of gold and emission spectrum of ceria offers another contribution to the enhancement of fluorescence intensity.Then, gold-ceria nanoparticles have been applied as optical sensing material for dissolved oxygen in aqueous media based on fluorescence quenching mechanism.The sensed data is automatically collected and processed through a wireless sensor network-based communication infrastructure with smartdata and feedback management capability.

The present work deals with the implementation of algorithms based on the techniques of optimization by ant colony (ACO) and Scatter Search (SS) together with the Finite Element method (MEF) for modeling and optimization of Tapers between a continuous 2D waveguide (CWG) and a periodically segmented 2D waveguide (PSW). The issue to be solved fits into combinatorial optimization problems, where in front of a large number of available subsets, it is possible to select the sets that produce the best coupling efficiencies. The proposed metaheuristics create new possibilities for optimizing and designing a variety of photonic devices for information processing.

Photomechanics, i.e., the conversion of light into thermal and mechanical work is of significant importance for energy conversion/reconfigurable technologies. Advantages of such photo-thermal mechanisms for transducers include remote energy transfer, remote controllability, control of actuation using number of photons (intensity) and photon energies (wavelength), fast actuation (milliseconds), low signal to noise ratio, high stored elastic strain energy densities with hyperelastic elastomers and scalability at different length scales using batch fabrication and high-volume semiconductor manufacturing. However, only a few materials exist that can convert light into mechanical work. Azobenzene liquid crystal elastomers were one of the first materials to exhibit the photomechanical effect. However, their application required two different light sources for reversible thermal switching (420 nm and 365 nm) between an extended trans and a shorter cis configuration. In this talk, we will cover how light is used with new materials to create the mechanical effect. New nanomaterials, when mixed with polymeric materials, show the unusual photomechanical effect that can be practically harnessed for real-world application. Straining new 2D nanomaterials such as graphene, MoS2 and others creates a new effect called the coupled straintronic photo-thermic effect enables large light absorption and also increase in mechanical effect. The talk will go through an overview of this new and upcoming area of research based on light-matter interaction in 1D and 2D nanomaterial composites

Photomechanics, i.e., the conversion of light into thermal and mechanical work is of significant importance for energy conversion/reconfigurable technologies. Advantages of such photo-thermal mechanisms for transducers include remote energy transfer, remote controllability, control of actuation using number of photons (intensity) and photon energies (wavelength), fast actuation (milliseconds), low signal to noise ratio, high stored elastic strain energy densities with hyperelastic elastomers and scalability at different length scales using batch fabrication and high-volume semiconductor manufacturing. However, only a few materials exist that can convert light into mechanical work. Azobenzene liquid crystal elastomers were one of the first materials to exhibit the photomechanical effect. However, their application required two different light sources for reversible thermal switching (420 nm and 365 nm) between an extended trans and a shorter cis configuration. In this talk, we will cover how light is used with new materials to create the mechanical effect. New nanomaterials, when mixed with polymeric materials, show the unusual photomechanical effect that can be practically harnessed for real-world application. Straining new 2D nanomaterials such as graphene, MoS2 and others creates a new effect called the coupled straintronic photo-thermic effect enables large light absorption and also increase in mechanical effect. The talk will go through an overview of this new and upcoming area of research based on light-matter interaction in 1D and 2D nanomaterial composites.

We will present interesting nano-engineered materials, ZnO nanocones (NCs) and their recent progress made in our group. The morphology of ZnO nanostructures was engineered to demonstrate enhanced optical and electrochemical characteristics of ZnO NCs compared to ZnO nanowires (NWs). ZnO NCs are obtained by chemically etching ZnO NWs. Hence, the morphological effects on various physical properties can be directly compared between NCs and NWs. In recent work of ours, electrochemical characteristics of ZnO NCs and NWs are extensively investigated to demonstrate morphology dependent capacitive performance of one dimensional ZnO nanostructures. Cyclic voltammetry measurements on these two kinds of electrodes in a three-electrode cell confirms that ZnO NCs exhibit a high specific capacitance of 378.5 F g−1 at a scan rate of 20 mV s−1, which is almost twice that of ZnO NWs (191.5 F g−1). In addition, ZnO NCs demonstrated enhanced optical properties, in particular much lower reflectance compared to NWs. We observed that optical properties are much enhanced from NCs compared to NWs. These observations suggest that ZnO NCs can be used main active materials for optical and energy devices.

MoS2, a representative 2D atomically thin semiconductor, has a sizable band gap leading to intensive research efforts to investigate its unique optical properties and realize a novel optoelectronic device based on MoS2. However, limited optical absorption in extremely thin MoS2 layers is an obstacle for high-efficiency light absorbing devices. In this work, we investigated how reflection and transmission phase-shift at the highly absorbing MoS2 interface could affect the absorption spectra of the MoS2 monolayers on SiO2/Si substrates (SiO2 thickness: 40 ~ 130 nm). Such interface-phase-shift gave rise to interference in MoS2 layer, although the layer thickness was only 0.7 nm, much smaller than the wavelength of the visible light. We compared measured and calculated optical reflection spectra, which showed that aforementioned interface-interference enhanced optical absorption in MoS2 monolayers. Raman intensity of MoS2 monolayers largely varied depending on the SiO2 thickness, which could be well explained by the calculated absorption in MoS2 layers. In addition, the interface-interference enabled omnidirectional absorption enhancement. This work showed that proper choice of the SiO2 thickness could provide us a simple and useful means to improve optical absorption in MoS2 monolayers.

We investigate the possibility of femto- or picoseconds pulse self-similar propagation in a medium containing noble metal nanorods. The main attention is devoted to the nonlinear chirped solitons propagation. Our investigation is bases on the semi-classical approach. Using this approach, we derive the set of equation, which describe the atomic states and electric field dynamics. We take into account non-stationarity of the density matrix elements, two-photon absorption of laser radiation and the non-stationary process of nanorods aspect ratio changing due to the nanorods reshaping under the action of laser radiation. On the basis of numerical calculations, we reveal the influence of the non-stationarity of the density matrix elements on the possibility of the laser pulse self-similar propagation in the medium with nanorods.

Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current transfer methods of 2D materials onto an arbitrary substrate deploy wet chemistry and viscoelastic stamping. However, these methods produce a) significant cross contamination of the substrate due to the lack of spatial selectivity b) may not be compatible with chemically sensitive device structures, and c) are challenged with respect to spatial alignment. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross contamination to the substrate. Our 2D printer-method results in an aerial cross contamination improvement of two to three orders of magnitude relative to state-of-the-art dry and direct transfer methods. Moreover, we find that the 2D material quality is preserved in this transfer method. Testing this 2D material printer on taped-out integrated Silicon photonic chips, we find that the micro-stamper stamping transfer does not physically harm the underneath Silicon nanophotonic structures such as waveguides or micro-ring resonators receiving the 2D material. Such accurate and substrate-benign transfer method for 2D materials could be industrialized for rapid device prototyping due to its high time-reduction, accuracy, and contamination-free process.

Great potential in medical applications makes that micro robot has been researched by several research groups. In this research, we demonstrates shape memory alloy (SMA) based micro robot. SMA wire, which has 25 μm of diameter, is cut and patterned by focused ion beam milling to fabricate shape of robot. The robot consists of diamond-shaped structures contracted and relaxed by two-way shape memory effect, and cuboid features that contact to ground. The robot is powered by ultraviolet laser and actuated using photothermal effect. It can move forward with speed of 2.5 μm/s. We anticipate that the SMA usage in micro robot can expand flexibility of material selection and enhance its functionality.

MoS2 and WS2 trilayers were grown on p-type Si wafers using atmospheric pressure plasma processes. Current-voltage measurements of MoS2/Si and WS2/Si heterojunctions showed rectifying behaviors, indicating formation of diodes. It should be noted that the very large shunt resistance indicated uniform MoS2 layer formation on the Si wafers. Relatively large dark current of the MoS2 and WS2 heterojunctions under reverse bias indicated the band to band tunneling and avalanche multiplication processes. Temperature dependence of the diode ideality factor was also studied to reveal the major recombination processes, based on conventional 3D semiconductor models. Photocurrent characteristics of the junctions were studied using green lasers (wavelength: 532 nm). Large photocurrent was observed under reverse bias, whereas photocurrent was negligibly small under forward bias. The measured photocurrent was linearly proportional to the laser power. This suggested that trapping and detrapping of the photo-generated carriers at interface defects and surface adsorbates did not much limit the collection of photo-carriers. Both MoS2/Si and WS2/Si heterojunctions showed fast photoresponse: the rising and decaying time constants were less than 0.1 ms. All these results showed that our processes could prepare high quality 2D/3D hybrid semiconductor heterojunctions with clean interfaces.

Optical up-conversion process using tri-valent lanthanide elements hosted by lowphonon environment is helpful in wide variety of biomedical, sensing, and optical-energy harvesting applications. In up-conversion process of erbium-based nanoparticles, infra-red photons have been absorbed and converted into visible light through two-photon absorption mechanism. In this work, erbium-doped ceria and Fluoride nanoparticles, of mean diameter around 10nm, are synthesized and optically-characterized through up-conversion process. Cerium oxide (ceria) and sodium-ytterium fluoride are selected as a host due to their relativelylow- phonon medium in addition to their conductive properties. The main optical core centers, erbium atoms, are responsible for optical conversion process of the range of ~520nm emission under 780nm excitation. Then, the synthesized nanoparticles are coated on the edges of frontside of silicon solar cell in addition to the backside. The optical efficiency improvement within the up-conversion process is expected due to better spectrum utilization. The backside coating is helpful to offer a conductive medium for the generated photoelectrons to be easier moved to the electrodes. The efficiency of solar cell is found to be improved due to the coated nanoparticles to 15.20% compared to the uncoated solar cell of 15%, with a clear increase in the value of short-circuit current.

The Ring-Core fiber (RCF) which can support several cylindrical vector beam (CVB) modes is desirable for future ultrahigh capacity space-division multiplexing (SDM). However, the size differs between adjacent CVB modes which result in mismatch in coupling. In this study, we design a simple and stable scheme to generate PPVs with adjustable orders and beam sizes. By changing the holograms encoded on the SLM, different sides PPVs of the same order can be obtained. We demonstrate PPVs range from +1 order to +9 order. Furthermore, with the employment of 25× object glass we couple the PPVs into graded-index Ring-Core fiber (GI-RCF) supporting 3 CVB mode-groups (i.e. HE21, HE31 and HE41) at 1550 nm wavelength. We also demonstrate the mode-groups (HE31 and HE41) transmitting over a 3m GI-RCF, respectively.

Micro-Lens Array (MLA) for diffusing incident light has been widely used for 3D depth measurement. Especially in Time-of-Flight (TOF) 3D sensor, output beam uniformity through the MLA is one of the most important factors to determine the sensor accuracy. This performance is highly related to a MLA lens structure. Randomized MLA, a substitute for regular periodic MLA, does not overcome a low diffusing efficiency due to the leaking light. To tackle this issue, we propose a new MLA design methodology which is comprised of various unit lenses having different curvatures and sizes (hereafter referred to as the “Mini-Lens"). The design method is to randomly overlap a sub lens having different curvatures and sizes into the regular periodic arrange. The Mini-Lens type MLA shows a non-periodic structure and no height difference. The experiments with our design show ~30% improvements in uniformity and efficiency compared to the regular periodic MLA and the randomly distributed MLA, respectively. New Mini-Lens can achieve a fill factor of 100% over various designed base and sub lens. In addition, the suggested methodology will be useful for designing all the structures that are difficult to arrange apart from rectangular and hexagonal type. Our methodology will be a new design method to overcome the limitation of its structure.

Ultrafine–grained copper was prepared by direct and equal-channel angular hydroextrusion. Tensile and stress relaxation tests were used to study the effect of microstructure on yield stress and strain-rate sensitivity of copper polycrystals in the insufficiently explored temperature range 4.2-295 K. Thermal activation analysis showed that in the range 77–200 K the rate of plastic deformation is controlled by the thermally activated mechanism of the forest dislocations intersection and its empirical parameters were obtained. Above 200 K the activation volume was decreased with the temperature increase. The inversion of the temperature dependence of the activation volume was attributed to the thermally activated detachment of dislocations from local pinning centers within the grain boundaries.

Publisher’s Note: This paper, originally published on 5 October 2018, was withdrawn on 28 June 2019 at the authors’ request.

Nation-wide, healthcare-associated infections (HAIs) infect one in every 25 hospital patients, account for more than 100,000 deaths and increase medical costs by around $96-147B, each year. Ultraviolet-C (UV-C) antimicrobial devices are shown to reduce the incidence of many of these HAIs by 35% or more, through the deactivation of the pathogen’s DNA chain following irradiation with a wavelength of ~254 nm. This irradiation does not kill the cells, per se but effectively prevents the cells from multiplying. Clinical case reductions of 30-70% in Clostridium difficile (C. diff.) have been reported with similar results for methicillin-resistant Staphylococcus aureus (MRSA), and others. The methodology works, but, the adoption of UV-C technology by the healthcare industry has been sporadic. This is largely due to the lack of definitive knowledge and uniform performance standards or measures for efficacy to help healthcare managers make informed, credible investment decisions. The leveling of the playing field with scientifically certifiable data of the efficacy of antimicrobial devices will enhance acceptance by the healthcare industry and public, at large, as well as facilitate science-based decision making.

The National Institute of Standards and Technology (NIST) has engaged with the International Ultra Violet Association (IUVA) and its member companies and affiliates to explore ways to develop needed standards, determine appropriate testing protocols, and transfer the technology to help to reduce these inharmonious market conditions. Collaborative efforts are underway to develop science-based answers to the healthcare industry’s questions surrounding standards and measures of device disinfection efficacy, as well as reliability, operations and durability. These issues were recently discussed at the IUVA 2018 America’s Conference in Redondo Beach, CA in several panel sessions. A major output of the sessions was the formation of a formal IUVA Working Group for the development of antimicrobial standards and initiatives for the healthcare industry. The goal of this working group is to provide global guidance, with specific programs and deliverables, on the use of UV technologies and standards to combat HAIs and to further the stated aims of the IUVA on its outreach to the healthcare industry. This paper reviews the strong collaboration between NIST and its industry partners pursuing the development of standards, guidelines and guidance documents related to healthcare applications that include standard methods for validating performance of UV devices and test guidelines for efficacy measurements. In addition, an overview of the issues, problems, and a summary of the needs confronting future growth and success of the UV industry in the Nation’s healthcare application space is provided.

In this work, we demonstrate an InGaAsP multiple quantum well tunable laser diode that amalgamates two gain sections with different bandgap energies. This tunable laser is used as a probing source for an optical sensor that makes use of surface plasmon resonance (SPR). The regions of different bandgap energies are achieved using selective area intermixing of the multiple quantum wells, through impurity-free vacancy induced disordering. By varying the current combination that was injected to each section, the laser wavelength can be effortlessly tuned from 1538 nm to 1578 nm with relatively constant output power. The free spactral range FSR of the tunable laser found to be 0.25 nm. This tunable laser was launched into an optical surface plasmon resonance sensor head that was fabricated on an inverted rib dielectric waveguide to provide an input light source for the SPR sensor. The average sensitivity of the SPR sensor devices was determined to be S = 334 nm.RIU-1.

There are numerous applications for pyroelectric composite films in the medical, military and environmental applications field. The main purpose (focus) of this research is to fabricate higher efficiency thin films that are flexible like polymers. Polystyrene has attracted the attention of scientists for its interesting features and its superior physical and chemical properties. A solution casting approach was developed to obtain flexible ZnO doped polystyrene (PS) nanocomposite thin films which were highly transparent in the visible region and exhibited excellent UV-absorbing properties. Major characteristics of this material include rigidity, transparency, high refractive index, good electrical insulation characteristics, low water absorption, and ease of processing which makes important for many applications in industry. Among the many inorganic materials, zinc oxide, ZnO, has been intensively studied as a promising material for optoelectronic devices such as light emitting diodes (LED). Optical characterization of the polystyrene think films doped with ZnO shows the reduction in the bandgap and enhancement in other optical properties.